1. Field of the Invention
This invention relates to a metal tubular body and its manufacturing method. More specifically, this invention relates to a metal tubular body having a wall thickness varying along its longitudinal axis which can be used in such applications as a pin, an injection needle, a connector, and a liquid crystal electron gun for TV, as well as its manufacturing method.
2. Prior Art
Metal tubular bodies of small diameter, for example, those having an inner diameter of up to 2 mm used as a pin, an injection needle, or a connector for medical applications, or an electron gun for TV is often required to have a wall thickness that varies from part to part. Such tubular body with varying wall thickness has been produced by using a tubular body having a constant thickness and grinding its outer or inner surface.
The tubular body manufactured by such method, however, suffered from the marks left on the surface that had been made in the grinding, and the resulting tubular body was defective. In addition, surface grinding was difficult to perform when the tubular body had a small diameter. Surface grinding also required an additional step, and resulted in a complicated manufacturing process that was unfeasible for mass production.
In spite of such situation, there is a practical need for a tubular body of smaller diameter. For example, patients requiring routine injection using an injection needle as in the case of diabetes patients conducing regular insulin injection are waiting for a needle wherein pain upon needle insertion has been reduced to its minimum.
An injection needle having an excessively reduced diameter, however, suffer from insufficient flow of the drug solution therethrough making the injection of the drug solution difficult. Accordingly, the diameter of the injection needle can be reduced only to a limited degree.
Tubular bodies having a varying diameter such as those having a tapered lateral shape or a stepped lateral shape have been manufactured by rolling a metal sheet, and repeatedly drawing the rolled metal sheet. The tubular body manufactured by such method, however, has a constant wall thickness along its full length despite the difference in the diameter. The wall thickness of such tubular body is, therefore, determined by the section of smallest diameter, and the tubular body manufactured inevitably suffers from insufficient strength since the section with a larger diameter has an excessively reduced wall thickness.
It is therefore an object of the present invention to obviate the prior art problems as described above and provide a metal tubular body having a varying wall thickness. Another object of the invention is to provide a method for manufacturing such metal tubular body.
In order to attain the object as described above, this invention provides a metal tubular body wherein at least a part of a wall thickness of the tubular body varies along its longitudinal axis, and wherein the tubular body has a minimum inner diameter of up to 2 mm and a maximum wall thickness of up to 0.5 mm.
The present invention also provides a method for manufacturing a metal tubular body wherein at least a part of a wall thickness of the tubular body varies along its longitudinal axis, comprising the steps of: punching a sheet blank in the developed shape of the tubular body from a metal sheet such that the metal sheet and the sheet blank remain partly joined, said metal sheet having at least a part of a thickness which varies in the direction of the longitudinal axis of the finished tubular body; pressing the sheet blank into a tubular shape; and cutting the pressed sheet blank from the metal sheet to thereby produce the tubular body.
The present invention also provides a method for manufacturing a metal tubular body wherein wall thickness of the tubular body varies along its longitudinal axis, comprising the steps of: punching a sheet blank in the developed shape of the tubular body from a metal sheet such that the metal sheet and the sheet blank remain partly joined; pressing the sheet blank into a tubular shape such that the pressed sheet blank in tubular shape has a thickness which varies along the longitudinal axis; and cutting apart the metal sheet and the sheet blank at the part where they remain joined to thereby produce the tubular body.
In the method for manufacturing a metal tubular body according to the present invention, the sheet blank that has been pressed in tubular shape may be welded along its seam.
This invention also provides a metal tubular body manufactured by the method of the present invention.